This invention relates to earth boring apparatus useful in the rotary system of boring holes in the earth, e.g. petroleum wells. Elements of such a system include a tubular drill string extending from the bottom of the bore to the surface and means at the surface for rotating the drill string and for raising and lowering same in the earth bore and for circulating drilling fluid, e.g. down the drill string and back up the bore annulus. At the lower end of the drill string is a drill bit. Borings and other detritus is carried to the surface by the drilling fluid and filtered out of the drilling fluid so it can be reused.
Detritus which is too dense to be carried away by the drilling fluid may be caught in a junk basket incorporated in the drill string. Examples of junk baskets are found in U.S. Pat. Nos.
______________________________________ 2,797,755 Bobo 2,894,725 Baker 3,198,256 Kirby. ______________________________________
A difficulty with junk baskets is that they must be disconnected from the drill string to be inverted to dump out the junk.
In order to keep the drill bit centralized in the well bore it is usual to provide a stabilizer just above the drill bit. In deep drilling where the drill bit may wear down and bore an undergage hole, instead of a stabilizer a reamer is provided just above the bit to ream the hole to at least full gage. The reamer also performs the function of a stabilizer and is sometimes called a reamer-stabilizer. Reamers may be of either the fixed blade type or the roller type. Examples of roller reamers with replaceable rollers are found in U.S. Pat. Nos.
______________________________________ 1,988,023 Spengler 2,189,034 Harrington 3,627,068 Wagnon. ______________________________________
There are limitations upon how much reaming can be done. For example, when the bit gets too worn it is apt to come apart in the hole. Or a reamer above a worn out bit may wear out rapidly and roller fragments or other parts fall into the hole. Broken bits and other metal parts are a frequently encountered form of detritus which must be removed by a junk basket.
In the case of modern carbide toothed roller cutter bits with sealed lubricated bearings, a limiting factor on bit life is often wear on a bit leg sufficient to damage a seal. Following loss of a seal lubricant is lost; then the bearing locks, cutter rotation stops, and bit efficiency is greatly reduced, wasting valuable rig time.
To avoid wearing the bit down too far, various devices have been contrived to signal to the driller that a bit change is in order. See for example, U.S. Pat. Nos.
______________________________________ 2,549,278 Yancey 2,560,328 Bielstein 2,562,833 Truz 2,580,860 Stokes 2,582,312 Del Homme. ______________________________________
It has also been proposed to provide above the bit a roller stabilizer having rollers with rough bands which will engage the well bore and increase the drill string torque when the earth bore diameter immediately above the drill bit becomes too small. The increased torque signals to the driller that it is time to change the bit. See U.S. Pat. No. 3,306,381 -- Garrett and Moore. However, this construction may be undesirable in that it places a heavy load on the bearing surfaces of the reamer rollers and their shafts. Also, when worn rollers are replaced the torque bands are discarded and wasted even if not worn out. * FNT * Compare U.S. Pat. Nos.
3,703,096 -- Vitter, Jr. (torque)
3,820,613 -- White (bearing block 4, inserts 8)
3,897,837 -- Peterson (carbide wear inserts 200)
It is also known to provide hard metal inserts or buttons on shoes formed on the legs or other body parts of a roller cone carbide tooth rock bit, e.g. for stabilization and wear reduction. See U.S. Pat. No. 3,628,616 -- Neilson and the advertisement:
"Introducing the `A-Team`"
Pages 24, 25, September 1977, issue of The American Oil & Gas Reporter.
However, such inserts or buttons have a radial extent determined by their function as stabilizers and wear reducers rather than as bit wear indicators. Even if viewed as torque-up buttons, such construction has the disadvantage that the buttons must be thrown away with the bit.
A further difficulty with previous tools is that a choice had to be made as to whether the junk basket, stabilizer, or torque indicator should be placed immediately adjacent to the bit, when it is desirable that all three should be so placed. Various combinations of reamers and junk baskets with other devices have been disclosed in U.S. Pat. Nos.
1,803,669 -- Grant -- reamer with expander
1,886,789 -- Carlson -- reamer and core bit
2,061,057 -- Bigler -- reamer with spring load
2,675,879 -- Middleton -- junk basket and bit
2,898,086 -- Freeman -- junk basket and bit.
None of these constructions integrates in one tool a wear indicator, a junk basket and a stabilizer.
It is an object of the invention to provide an earth boring apparatus which will overcome the aforementioned difficulties with reamers, junk baskets and wear signalling devices.